NIC teaming lets you increase the network capacity of a virtual switch by including two or more physical NICs in a team. To determine how the traffic is rerouted in case of adapter failure, you include physical NICs in a failover order. To determine how the virtual switch distributes the network traffic between the physical NICs in a team, you select load balancing algorithms depending on the needs and capabilities of your environment.
NIC Teaming Policy
You can use NIC teaming to connect a virtual switch to multiple physical NICs on a host to increase the network bandwidth of the switch and to provide redundancy. A NIC team can distribute the traffic between its members and provide passive failover in case of adapter failure or network outage. You set NIC teaming policies at virtual switch or port group level for a vSphere Standard Switch and at a port group or port level for a vSphere Distributed Switch.
Load Balancing Policy
The Load Balancing policy determines how network traffic is distributed between the network adapters in a NIC team. vSphere virtual switches load balance only the outgoing traffic. Incoming traffic is controlled by the load balancing policy on the physical switch.
For more information about each load balancing algorithm, see Load Balancing Algorithms Available for Virtual Switches.
Network Failure Detection Policy
You can specify one of the following methods that a virtual switch uses for failover detection.
- Link status only
Relies only on the link status that the network adapter provides. Detects failures, such as removed cables and physical switch power failures. However, link status does not detect the following configuration errors:
- Physical switch port that is blocked by spanning tree or is misconfigured to the wrong VLAN .
- Pulled cable that connects a physical switch to another networking devices, for example, an upstream switch .
- Beacon probing
Sends out and listens for Ethernet broadcast frames, or beacon probes, that physical NICs send to detect link failure in all physical NICs in a team. ESXi hosts send beacon packets every second. Beacon probing is most useful to detect failures in the closest physical switch to the ESXi host, where the failure does not cause a link-down event for the host.
Use beacon probing with three or more NICs in a team because ESXi can detect failures of a single adapter. If only two NICs are assigned and one of them loses connectivity, the switch cannot determine which NIC needs to be taken out of service because both do not receive beacons and as a result all packets sent to both uplinks. Using at least three NICs in such a team allows for n-2 failures where n is the number of NICs in the team before reaching an ambiguous situation.
By default, a failback policy is enabled on a NIC team. If a failed physical NIC returns online, the virtual switch sets the NIC back to active by replacing the standby NIC that took over its slot.
If the physical NIC that stands first in the failover order experiences intermittent failures, the failback policy might lead to frequent changes in the NIC that is used. The physical switch sees frequent changes in MAC addresses, and the physical switch port might not accept traffic immediately when an adapter becomes online. To minimize such delays, you might consider changing the following settings on the physical switch:
- Disable Spanning Tree Protocol (STP) on physical NICs that are connected to ESXi hosts .
- For Cisco based networks, enable PortFast mode for access interfaces or PortfFast trunk mode for trunk interfaces. This might save about 30 seconds during the initialization of the physical switch port.
- Disable the trunking negotiation.
Notify Switches Policy
By using the notify switches policy, you can determine how the ESXi host communicates failover events. When a physical NIC connects to the virtual switch or when traffic is rerouted to a different physical NIC in the team, the virtual switch sends notifications over the network to update the lookup tables on physical switches. Notifying the physical switch offers lowest latency when a failover or a migration with vSphere vMotion occurs.